Dense wavelength division multiplexing (DWDM) is a technology that combines a group of optical wavelengths for transmission over one fiber. This technology can increase bandwidth of an existing fiber backbone network, and in a case in which a given information transmission capacity is unchanged, a total quantity of required fibers can be reduced.
As requirements on throughputs of switching nodes on a metropolitan area network and a backbone network in a wavelength division multiplexing (WDM) optical network become higher, the speed of a single wavelength also becomes higher. After a coherence technology is introduced, complexity and costs of a wavelength adding/dropping and wavelength conversion device increase sharply. Therefore, an optical cross-connect node needs to use a wavelength adding/dropping and wavelength conversion structure shared in multiple dimensions. In a used large-scale optical switch, wavelengths in each dimension are expanded, and switching and adding/dropping are performed in the optical switch, so that sharing of wavelength adding/dropping and wavelength conversion may be implemented. However, due to process difficulty of a large-scale optical switch, a quantity of optical switch ports in the industry far cannot satisfy requirements of the backbone network. In addition, by using a combination of some small optical switches, wavelength adding/dropping and wavelength conversion may also be shared in multiple dimensions.
An optical switching method based on a wavelength plane is available in the prior art. WDM light from various dimensions is separated through wavelength division demultiplexing, and then a same wavelength is sent to a same small switch (that is, a wavelength plane). Light of each wavelength is groomed in a respective wavelength plane. After grooming is complete, the WDM light in each dimension is multiplexed. In each wavelength plane, particular input and output ports are reserved for wavelength adding/dropping and wavelength conversion, and the reserved ports are connected to a wavelength conversion switch. The wavelength conversion switch also reserves particular ports for wavelength adding/dropping. When a wavelength needs to be dropped, the wavelength enters the wavelength conversion switch from a reserved output port of a corresponding wavelength plane, and then is output from the wavelength conversion switch to a wavelength dropping port. When a wavelength needs to be added, the wavelength is added from a wavelength adding port of the wavelength conversion switch, sent to a corresponding wavelength plane through the wavelength conversion switch, and switched in the corresponding wavelength plane to a target dimension. When a wavelength needs to be converted, the wavelength is dropped from a reserved port of a corresponding wavelength plane and arrives at the wavelength conversion switch, and after wavelength conversion is complete, is switched to a target wavelength plane, and then groomed to a corresponding wavelength plane.
In the foregoing optical switching method based on a wavelength plane, because particular ports need to be reserved in each wavelength plane for wavelength adding/dropping, when a proportion of wavelength adding/dropping to wavelength conversion is relatively high, a case in which a particular wavelength needs to be completely added or completely dropped is likely to occur. Therefore, a sufficient number of ports need to be reserved in each wavelength plane, and correspondingly, the wavelength conversion switch also needs to have a large quantity of ports. If an optical switch is used for implementation, it is difficult to implement this according to a process in the industry. However, if the quantity of reserved ports in each wavelength plane is relatively small, a packet loss is likely to be caused. In addition, the ports in the wavelength plane are fixedly used for wavelength grooming, but the ports in the wavelength conversion switch can be fixedly used only for wavelength adding/dropping and wavelength conversion. Therefore, if there are too many ports in the wavelength conversion switch, resource waste is likely to be caused, and flexibility is poor.